1. Field of the Invention
The invention relates generally to optical bottle checkers. In particular, the invention relates to a programmable, automatic optical bottle checker.
2. Background Art
There are many well known devices for checking for flaws or defects in glass containers, hereafter simply called bottles. One type of bottle checker is disclosed by Powers in U.S. Pat. No. 3.557,950. Improvements of this bottle checker are disclosed by Powers in U.S. Pat. No. 3,690,456 and by Bryant et al in U.S. Pat. No. 4,213,702. The mechanics of this system are briefly summarized here. Bottles are conveyed along a conveyor line past a checking station. At the checking station, a carriage moves reciprocally along the conveyor line in synchronism with the bottles. The carriage grasps the bottle and then rotates it. As schematically illustrated in FIG. 1, as a bottle 10 is being rotated by the moving carriage several light sources 12 (only one is here illustrated) shine light toward the bottle 10. At least one light sensor 14 is carried by the carriage and is positioned at the side of the rotating bottle 10, and other light sensors may be provided. A probe 16 may be inserted into the neck of the bottle 10 to check for flaws on the bottle lip. The level of each photosensor output is proportional to the light transmitted through the bottle to that photosensor. or alternatively to the amount of light reflected from the bottle to that photosensor. The outputs of the various light sensors are supplied to a checker electronics system. If there are flaws in the bottle 10, then the flaws cause uneven reflection or transmission of light as the bottle is rotated. Powers '950 checks to determine if the light level is above a threshold value, whereas Bryant et al '702 checks to determine if the difference between the outputs of two sensors at spaced apart locations exceeds a threshold. The checker electronics system 18 then determines that an unacceptable flaw is present in the bottle 10 and rejects that bottle.
Although an embodiment of the checker electronics system 18 is disclosed in the first Powers patent, an improved electronics system usable with the Powers bottle checker is disclosed by Claypool in U.S. Pat. No. 4,488,648. The two Powers patents and the the Claypool U.S. Pat. No. are incorporated herein by reference. A bottle checking system implementing these three patents is available from Powers Manufacturing. Inc. of Elmira. N.Y.
The Claypool electronics system is controlled by a microcomputer. The sensor outputs are sampled 416 times for a 405.degree. rotation of the bottle, and the samples are digitized and stored in a data memory. The electronics then compares the digitized data and, if there is a difference therebetween which is greater than a set threshold, the bottle is rejected. In the disclosed system, the data memory contains four data samples with the oldest and newest samples being compared. The difference between compared samples, analogous to the slope of the change in the photosensor output, is then compared to a manually set threshold level.
One of the drawbacks of the Claypool system is that the threshold value needs to be programmed into the electronics system based upon whether the system rejects bottles having known flaws. That is, the set up is by trial and error. Both a "good" bottle and a flawed bottle are passed through the system with continual adjustments of the threshold value until the good bottle is passed and the flawed bottle is rejected. This process needs to be repeated for each photosensor and for each different type of flaw. If the bottle checker is used on a production line changing between different types of bottles, the complexity of the set-up causes production inefficiencies.
Furthermore, the slope comparison method of Claypool suffers from the disadvantage that the slope is dependent upon the speed of rotation of the bottle. Thus, if the bottle production rate is changed, the threshold needs to be changed if anomalies and flaws are to be consistently distinguished. Similarly, for a small diameter container, a much lower threshold is required than for large diameter containers.
Another drawback of the Claypool system, is that the reject criterion is a simple comparison of the slope of the light signal against a threshold. Although there are other prior art bottle checkers which reject a bottle only when the light interruption persists for a threshold duration, it is felt that the reject criterion is still too simple to adequately reject known types of flaws while accepting other aberrations in the bottle which are not true defects.
Yet further, there is a need for faster analog-todigital conversion in converting the outputs of the photosensors to a form usable in digital processing in the checker electronics. There is also a need for a wider range of amplification gain for the photosensor outputs.